Interference is a major bottleneck in wireless systems design. The performance of each user or link in a wireless network depends not only on its own transmission, but also on the interference coming from other links or users' transmissions. When one user tries to improve its performance by increasing its transmitted power, it automatically generates more interference for other users, thereby degrading their performance. To combat interference, traditional technologies service multiple users within each cell by distributing them over orthogonal dimensions, e.g. in different time slots as in Time Division Multiple Access (TDMA) systems, or over different frequency bands as in Frequency Division Multiple Access (FDMA) systems, or by spreading them across time and frequency as in Code Division Multiple Access (CDMA) systems.
Developing and optimizing more advanced, yet practical, interference mitigation techniques becomes particularly important nowadays, due to the rapid pace of growth of wireless networks and their enormous data usage, and the scarcity of the available radio resources, e.g. bandwidth and transmit power.
The performance of future (next generation) wireless networks is therefore expected to depend strongly on the feasibility of the dynamic power spectrum optimization methods, specifically developed to minimize or even to eliminate interference, as a means to achieving higher data capacity and increase system reliability.
In particular, there is a need to address resource allocation problems and provide a practical optimization method to decide which user should be served over a particular frequency tone in an orthogonal frequency division multiple access (OFDMA) system, and which transmit power should be allocated at each specific tone.
The problems of scheduling and power control have been extensively considered in the past, both separately and jointly, e.g., in copending PCT patent publication No. WO/2011/037319, published 31 Mar. 2011, by T. Kwon, W. Yu, C. Shin, and C. Hwang, entitled “Method and Device for User Scheduling and Managing Transmit Power in a Communication System”. (Kwon et al.), in an article by L. Venturino, N. Prasad, and X. Wang, entitled “Coordinated Scheduling and Power Allocation in Downlink Multicell OFDMA Networks,” IEEE Trans. Veh. Technol., vol. 6, no. 58, pp. 2835-2848, Jul. 2009 (Venturino et al.), and in an article by A. L. Stolyar and H. Viswanathan, entitled “Self-Organizing Dynamic Fractional Frequency Reuse for Best-Effort Traffic Through Distributed Inter-Cell Coordination,” in INFOCOM, April 2009 (Stolyar et al.). These references will be referred to again in the following paragraphs simply as references Kwon et al., Venturino et al. and Stolyar et al., respectively.
For the power spectrum optimization problem in an OFDMA network, the main challenge has always been to find computationally efficient methods to allocate the power of the different transmitters across the different frequency tones. The work described in Kwon et al., which proposes a power adaptation method based on Newton's method (NM), is particularly relevant to this problem. The method described in Kwon et al. shows a significant gain compared to the most straightforward method of transmitting at the maximum allowable power for all transmitters across all tones. The method in Kwon et al. is, however, both computationally complex, and relatively slow in convergence, albeit being faster than previously proposed methods.
Thus, there is a need for novel, feasible, and practical methods for power spectrum optimization. While interference mitigation is advantageous for all types of wireless communication systems, it is particularly relevant to the development of next-generation wireless backhaul products for compact base-stations, and Non Line of Sight (NLOS) type of backhaul networks, for example. NLOS backhaul technology provides a cost-effective wireless NLOS method to increase the cell site capacity of PicoCell and MicroCell deployments. In a system of this type, a cellular network may comprise several PicoCells, each covering a relatively small area, as a means to increase the network capacity for areas with dense data traffic. The users within each PicoCell are served by their own PicoCell base-station, also called access modules (AM). The AMs are collocated with the remote backhaul modules (RBM). Each RBM is connected to some central base-stations, also known as the hubs, via wireless backhauls links which are meant to replace the expensive optical fiber links. The hubs are responsible for the transmission strategies and radio resource management for the different RBMs. Unlike the classical relay problem, the backhaul architecture assumes that the wireless backhauls links and the access links operate at different frequencies. From a backhaul design perspective, the interest is therefore mitigating the interhub interference, thereby maximizing the aggregate data capacity of the RBMs.
NLOS backhaul technology has been an area of considerable research and development activity of late. In particular, the above referenced copending PCT application and US patent application claiming priority from U.S. provisional application No. 61/382,217 (Beaudin), disclose a method for measuring the co-channel interference in a NLOS environment, and for scheduling resources based on measured co-channel interference data. This method is referred to herein as managed adaptive resource allocation (MARA). In particular embodiments, the methods disclosed in Beaudin comprise measuring data indicative of interference, e.g. the channel gain, between each hub and each RBM Unit, periodically during active service. The corresponding measurements can be thought of, or represented, as a channel matrix whose entries describe the frequency domain channel gains between each hub and each RBM of the interference environment. This matrix of measurements, e.g. frequency domain channel gains will be referred to herein as a MARA matrix. In Beaudin, the MARA matrix is used, for example, to intelligently group each RBM to its most favorable hub, as well as to allocate resource blocks in such a way as to reduce interference between links and optimize aggregate capacity of the network, so as to organize the network resources in an optimal configuration.
An object of the present invention is to provide improved or alternative methods for interference mitigation, with scheduling and power allocation, which may be particularly applicable for NLOS wireless backhaul networks. There is a particular need to derive practically feasible methods for power spectrum optimization, with lower complexity and faster convergence than the Newton methods disclosed in Kwon et al. It would also be beneficial to take advantage of the measurements in an active network, such as disclosed in Beaudin, for novel or improved interference mitigation and/or power control methods.